A mechanical press including a correcting apparatus for the slide bottom dead point position

Abstract: A correcting apparatus for slide bottom dead point position of mechanical press which is capable of automatically correcting the slide bottom dead point position rapidly and accurately even during the operation of the mechanical press with the die-height adjusting screw mechanism being fixed. The correcting apparatus of the present invention comprises a hollow cylindrical member which is disposed between a slide and a die-height adjusting screw mechanism and which can be reverted or contracted along the axis thereof, a bottom dead point position setting means, a bottom dead point position detecting means for detecting a slide bottom dead point position with respect to the slide, contraction force applying means which supply contraction force to the hollow cylindrical member so that the hollow cylindrical member can be reverted or contracted, and correction control means which control the driving of the contraction force applying means to revert or contract the hollow cylindrical member in order to correct the slide bottom dead point position so that a detected bottom dead point position coincides with a set bottom dead point position.

Description: BACKGROUND OF THE INVENTION Field of the Invention Mechanical presses produce heat during their operation. As a result, the temperatures of respective parts increase and if the mechanical press is stopped, the temperature thereof drops to the ambient temperature because of the radiation of heat. However, the degrees of the rise and drop of the temperatures thereof differ depending on the respective components constituting the mechanical press. Thus, differences of the temperatures are produced among the respective parts so that differences in the amount of heat expansion occur among the respective parts because of the differences of the temperatures. The position of the bottom dead point of the slide is changed because of the differences in the amount of heat expansion. Consequently, the die height of the mechanical press is changed. The change of the die height adversely affects the accuracy of parts which are produced by the press. The present invention relates to means for minimizing the change of the die height or the change of the bottom dead point of the slide in order to obtain highly accurate parts. Description of Related Art The following methods for minimizing the change of the bottom dead point of the slide have been proposed. a) A method for splashing oil of a predetermined temperature on connecting rods in which the change of the temperature is large (Japanese Patent Publication No.1-30569) has been proposed. According to this method, it is difficult to maintain the position of the bottom dead point of the slide accurately when the mechanical press is operated with changes in the amount of generated heat, for example, when the press speed is changed or when the cycle of operation startup/stop and the duration time are changed. b) A method has been proposed in which a stopper block is disposed between the slide and the bed so that they correspond to each other and in which the stopper block is hit each time when the bottom dead point is reached in order to restrict the position of the bottom dead point (Japanese Patent Publication No.1-55056). According to this method, although the position of the bottom dead point can be restricted accurately if the elasticity of the stopper block is high, the changes of load applied to the mechanical press because of the high elasticity increase so that the mechanical press may be damaged. If the elasticity of the stopper block is low, it is not possible to control the position of the bottom dead point accurately. c) A method for determining the position of the bottom dead point at a constant position using a die-height adjusting device shown in Fig.6 employs a connecting rod 11P, a lock nut 22P, a slide 4, an adjusting screw 16P, worm shaft 18, worm wheel 19P and other parts. Although the lock nut 22P is fixed to eliminate the influence of threads between the connecting rod 11P and the adjusting screw 16P, the die height cannot be adjusted until the lock nut 22P is loosened. Because it is not possible to eliminate influences of the clearance of the threads if the lock nut 22P is loosened, the mechanical press must be stopped during the adjustment of the die height. Further, because the amount of the accurate adjustment for determining the bottom dead point at a constant position is fine as compared with the amount of the adjustment of the die-height which is ordinarily performed for die exchange or the like in order to minimize the changes of the die-height due to heat generated during the operation and the treatment of the lock nut 22P is necessary, the accurate adjustment is difficult and it takes long time to perform the adjustment. As described above, there have been no means by which the changes of the bottom dead point can be adjusted accurately regardless of whether the press is running or stopping, and conventional means lack part of the required functions. SUMMARY OF THE INVENTION An object of the present invention is to provide a mechanical press including an apparatus for correcting the slide bottom dead point position by which it is possible to eliminate the disadvantages of the prior method. This object is achieved by the features of claim 1. Preferred embodiments of the invention are subject matter of the dependent claims. The die-height adjusting device includes an adjusting screw locking mechanism, and shrink means and contraction force applying means are incorporated between the die-height adjusting device and the slide. The adjustment of the die-height which is performed during the down time of the mechanical press for die exchange or the like is performed by means of the die-height adjusting device equipped with the same locking mechanism as in the prior art. Fine adjustment for setting the bottom dead point at a constant point is performed by expanding or contracting the shrink member which elastically expands or contracts in the direction for changing the bottom dead point by means of the contraction force applying means. The shrink member can be expanded or contracted during the running of the mechanical press as well as when the press is stopping. The releasing of the fixing of the adjusting screw which is performed during the stopping time of the mechanical press is performed by releasing the contraction force applying means and the fixing thereof is achieved by actuating the contraction force applying means. Set values and detected values are input to a control apparatus by the bottom dead point setting means for setting an objective bottom dead point position and a bottom dead point position detecting means for detecting the bottom dead point position of the slide. The control apparatus perform arithmetic operation on the basis of the entered set value, detected value and values relative to previously entered elastic contraction. The control apparatus controls the driving of the contraction force applying means according to the result of the arithmetic operation to expand or contract the shrink member and adjust the bottom dead point position of the slide thereby maintaining the die-height accurately. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a sectional view for explaining the main parts of an embodiment of the present invention. Fig.2 is a view for explaining an hydraulic pressure supplying means and correction control means which constitute the contraction force applying means. Fig.3 is a view for explaining a mechanical press which employs the bottom dead point correcting apparatus of the present invention. Fig.4 is a view for explaining the relationship between the internal pressure of a cylinder apparatus and the amount of the deformation of the hollow cylindrical member. Fig.5 is a diagram for explaining the second embodiment of the present invention. Fig.6 is a sectional view for explaining a conventional bottom dead point position correcting apparatus. (Description of Reference Numerals) 4: slide, 5: bolster, 11: connecting rod, 20: hollow cylindrical member (shrink member), 21: bolt member (contraction force applying means), 22: lock nut, 30: cylinder device (contraction force applying means), 30A: piezo actuator (shrink member), 40: control panel, 41: control section (correction control means), 42: signal comparing means (correction control means), 43: bottom dead point setting means, 44: latch circuit, 45: bottom dead point position detecting means, 46: high voltage power supply (contraction force applying means), 47: charge input circuit (contraction force applying means), 48: charge releasing circuit (contraction force applying means), Ps: set bottom dead point position signal, Pi: actual bottom dead point position signal, S1: deviation signal for contraction, S2: deviation signal for expansion DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the accompanying drawings. First embodiment The first embodiment of the bottom dead point position correcting apparatus according to the present invention comprises shrink members 20, contraction force applying means 21, 30, 36 or the like, and a correction control means 41, 42. Each of the shrink members 20 is expanded or contracted to automatically adjust the change of the bottom dead point position. The same reference numerals are attached to the components common to a conventional example shown in Fig.6 and the description thereof is omitted or simplified. A mechanical press containing an apparatus of the present invention will be described with reference to Fig.3. Referring to Fig.3, reference numeral 1 designates a crown, numeral 2 designates a column and numeral 3 designates a bed. A crank shaft 10 having eccentric portions 10e, 10e is rotatably supported within the crown 1. A fly wheel 12, a clutch 13C and a brake 13B are mounted on the crank shaft 10. The clutch 13C transmits a driving power from the fly wheel 12 to the crank shaft 10. A driving power source (not shown) for driving the fly wheel 12 is connected to the fly wheel 12. A slide 4 is connected to the eccentric portion 10e of the crank shaft 10 through connecting rods 11 and hollow cylindrical members 20 or the like. A bolster 5 is mounted on the bed 3. An upper die (not shown) is fixed on the bottom surface of the slide 4. On the other hand, a lower die (not shown) is fixed on the bolster 5. The position of the aforementioned slide 4 is vertically adjustable by means of a die-height adjusting screw mechanism of a known slide position adjusting device and the slide 4 is fixed after the adjustment is finished. As shown in Fig.1, the die-height adjusting screw mechanism comprises an adjusting screw shaft 16 which includes a spherical bearing 17 engaging with a spherical body 11B provided on the bottom end of the connecting rod 11 and which is connected with the worm wheel 19, a lock nut 22 for fixing the adjusting screw 16, a worm screw shaft 18 which is engaged with the worm wheel 19, a motor (not shown) for driving the screw shaft 18, and a hollow cylindrical member 20 in which the upper portion thereof is engaged with the adjusting screw shaft 16 through screws 16S, 20S and in which the bottom portion thereof is fixed to the slide 4 through a cylinder device 30. Thus, if pressurized oil within a cylinder chamber 32 described above is released to eliminate the tightening force of the bolt member 21 thereby loosening a lock nut 22 and the worm screw shaft 18 is rotated, the male screw 16S of the adjusting screw shaft 16 is rotated with respect to the female screw 20S of the hollow cylindrical member 20 fixed to the slide 4 through the worm wheel 19 and a pin member 29 inserted through the worm wheel 19 and the adjusting screw shaft 16, so that it is possible to adjust the bottom dead point position by moving the slide 4 vertically. In Figs.1 and 3, reference numeral 15 designates a case and numeral 14 designates a guide member. The shrink member constituting the bottom dead point position correcting apparatus of the present invention is provided between the slide 4 and the die-height adjusting mechanism so as to be able to expand or contract along the axis. In this embodiment, the shrink member comprises the hollow cylindrical member 20 which constitutes the die-height adjusting screw mechanism. The bottom dead point position adjusting means is formed to set a bottom dead point position indirectly according to the die-height. The bottom dead point position adjusting means comprises digital switches and outputs a set bottom dead point position signal Ps. The bottom dead point position detecting means 45 is used for detecting the bottom dead point position of the slide 4. The bottom dead point position detecting means 45 according to the present invention employs known high-frequency oscillating type eddy-current detecting method. According to this method, the position of the slide 4 with respect to the bolster is output using absolute type electric signals. The contraction force applying means is a means for elastically expanding the hollow cylindrical member 20 by applying contraction force to the hollow cylindrical member 20 of the shrink member and comprises a bolt member 21, a cylinder unit 30 and a hydraulic pressure supplying port 34 of the hydraulic pressure supply means, a directional control valve 36, hydraulic supply source (not shown) or the like. The cylinder unit 30 comprises a cylinder 31 which is provided on the slide 4 and a piston 33 which is incorporated within a cylinder chamber 32 of the cylinder 31 so that the piston 33 is vertically movable. The aforementioned cylinder 31 has a hydraulic pressure supply port 34 for supplying hydraulic pressure in between the top face of the cylinder chamber 32 and the piston 33. The bolt member 21 is installed within the hollow cylindrical member 20 and the bolt member 21 can move vertically with respect to the hollow cylindrical member 20. The bottom end thereof is fixed to the piston 33 and the top end thereof is integratedly connected to the hollow cylindrical member 20 and the lock nut 22. The hydraulic pressure supply means is formed so as to be able to supply hydraulic pressure of a predetermined pressure (minimum pressure Pr0 - maximum pressure Pr2) value into the cylinder chamber 32 of the cylinder unit 30. The hydraulic pressure supply means is provided in the hydraulic pressure source (not shown) and a pipe connecting the hydraulic pressure source with the hydraulic pressure supply port 34 of the cylinder 31, and comprises an electric hydraulic pressure servo valve 36 with electric hydraulic pressure servo mechanism for controlling the internal pressure of the cylinder chamber 32 in proportion to electric input signal, a pressure sensor 35, a servo amplifier and the like. When hydraulic pressure is supplied into the cylinder chamber 32, the bolt member 21 is pulled and stretched because the top end thereof is fixed to the hollow cylindrical member 20 through the lock nut 22, so that the hollow cylindrical member 20 is forced so as to contract. As a result, the slide 4 is moved upward by the amount of the contraction of the hollow cylindrical member 20. The relationship between the internal pressure Pri of the cylinder unit 30 and the amount of the contraction δ is determined by a diagram shown in Fig.4. That is, if the internal pressure Pri of the cylinder chamber 32 is changed from the minimum pressure value Pr0 to the maximum pressure value Pr2, the hollow cylindrical member 20 is deformed by the maximum amount of the deformation ( b - a = δ ). Thus, if an intermediate value (substantially medium value) between the aforementioned Pr0 and Pr2 is applied within the cylinder chamber 32 as the initial internal pressure Pr1 and then the internal pressure is increased from that condition, the hollow cylindrical member 20 is contracted by the amount of the increase of the internal pressure. Conversely, if the internal pressure Pri is reduced from the initial pressure Pr1, the hollow cylindrical member 20 is expanded by the amount of the decrease of the internal pressure. The amount of contraction δ of the hollow cylindrical member 20 with respect to an arbitrary internal pressure Pri (Pr0≤Pri≤Pr2) is calculated according to the value of an arbitrary internal pressure Pri. In the present embodiment, the aforementioned internal pressure Pr1 is selected so as to be a middle value between the minimum amount of contraction of the hollow cylindrical member 20 and the maximum amount of contraction thereof. Thus, even if the bottom dead point position changes upward or downward, it is possible to correct the position accurately. The correction control means controls the driving of the contraction force applying means so as to make a detected bottom dead point position coincide with a set bottom dead point and then expands or contracts the hollow cylindrical member 20 of the shrink member in order to correct the slide bottom dead point position. The correction control means comprises a control unit 41 of a control panel 40 and a signal comparison means 42 as shown in Fig.2. The signal comparison means 42 compares the set bottom dead point position signal Ps from the bottom dead point setting means 43 with the actual bottom dead point position signal Pi from the bottom dead point detecting means 45, and if Ps>Pi, the signal comparison means 42 outputs the deviation signal (contraction signal) S1. If Ps<Pi, the signal comparison means 42 outputs the deviation signal (expansion signal) S2 to drive the electric hydraulic type servo mechanism (35, 36, etc.). The signal comparison means 42 is contained in the control panel 40. The signal comparison means 42 is not restricted to the aforementioned case, but if a previous actual bottom dead point position signal and a current bottom dead point position signal are assumed to be Pi and Pj, respectively, the signal comparison means 42 outputs the deviation signal S1 when (Ps - Pi)<(Ps - Pj) and outputs the deviation signal S2 when (Ps - Pi)>(Ps - Pj) . When the signal comparison means 42 outputs the deviation signal S1, the servo valve 36 is actuated so that hydraulic pressure of a pressure value proportional to the deviation input signal e is supplied into the cylinder chamber 32 of the cylinder unit 30. The internal pressure Pri of the cylinder chamber 32 is detected by means of the pressure sensor 35. If the internal pressure Pri reaches a pressure value (>Pr1) corresponding to the deviation signal S1 [namely, a deviation (e) between a feedback signal fi from the pressure sensor 35 and the deviation signal S1 becomes 0], the supply of hydraulic pressure is stopped and the internal pressure Pri is maintained at a pressure value (>Pr1) which corresponds to the deviation signal S1. If the signal comparison means 42 outputs the deviation signal S2, the hydraulic pressure of the cylinder chamber 32 is discharged through the servo valve 36 until the hydraulic pressure of the cylinder chamber 32 decreases to a pressure value (<Pr1) corresponding to the deviation signal S2. The control unit 41 is constructed so as to output a latch signal to a latch circuit 44 when the crank angle of the mechanical press coincides with a set crank angle corresponding to the bottom dead point, thereby maintaining the actual bottom dead point position signal Pi from the bottom dead point position detecting means 45, determining the actual bottom dead point position signal Pi for comparison and outputting a control signal in order to make the signal comparison means 42 perform the comparison of signals. Thus, it is possible to automatically correct changes of the bottom dead point with respect to the actual bottom dead point rapidly for each slide stroke. Next, the operation of the present embodiment will be described. Pressurized oil within the cylinder chamber 32 is released to eliminate the tightening force of the bolt member 21 thereby loosening the lock nut 22. After this, the die-height adjusting screw mechanism is actuated to adjust the vertical relative position of the slide 4 with respect to the connecting rod 11, thereby adjusting the die-height corresponding to a used die. Correspondingly, the slide bottom dead point position is set using the bottom dead point setting means 43. In this case, the output signal of the bottom dead point position detecting means 45 or the actual bottom dead point position signal Pi is adjusted so as to be the same as the set bottom dead point position signal Ps which is output from the bottom dead point position setting means 43. If the mechanical press starts, so that the crank angle becomes the same as a set crank angle (bottom dead point position), the control unit 41 outputs a latch signal to the latch circuit 44, thereby maintaining the actual bottom dead point position signal Pi from the bottom dead point position detecting means 45 as the actual bottom dead point position signal Pi for comparison and outputting a control signal to the signal comparison means 42. The signal comparison means 42 compares the set bottom dead point position signal Ps with the bottom dead point position signal for comparison. The temperature of the machine does not change for a while after the startup of the mechanical press and the relationship of Ps = Pi is maintained, no deviation signals S1, S2 are output. Thus, the clearance between the upper die and the lower die at the bottom dead point is maintained at a set value in order to produce products having a predetermined accuracy smoothly. Next, consider a case in which the position of the bottom dead point is changed due to changes of the temperature and other parts. Assume that when the crank angle becomes a set crank angle, the position of the slide 4 becomes lower than its predetermined position, that is, the clearance between the slide 4 and the bolster 5 becomes smaller than the set value thereof. The value of the actual bottom dead point position signal Pi is lower than the set bottom dead point position signal Ps, so that the relationship of Ps>Pi is presented. Under this condition, it is not possible to maintain a clearance between the lower die and the upper die at the bottom dead point so that the accuracy of products is deteriorated. According to the present invention, the signal comparison means 42 outputs the deviation signal S1 for contraction. Receiving the deviation signal, the servo mechanism (35, 36, etc.) is actuated and then the internal pressure Pri of the cylinder chamber 32 becomes a pressure value (>Pr1) corresponding to the deviation signal S1. Consequently, the hollow cylindrical member 20 is pushed so as to contract and the slide 4 is moved upward by the amount corresponding to the deviation signal S1. As a result, the change of the bottom dead point position can be automatically corrected. This correcting action is performed each time when the crank angle becomes the set crank angle. On the other hand, if the temperature of the mechanical press changes suddenly because the mechanical press stops temporarily, press speed changes due to decrease of the power supply voltage or the like, the bottom dead point position sometimes changes upward. In these cases, the relationship of Pi<Pj is maintained. Namely, a difference (Ps - Pj) between the actual bottom dead point position signal value Pj and the set bottom dead point position signal Ps becomes smaller than a previous difference (Ps - Pi). Consequently, the signal comparison means 42 outputs the deviation signal S2 for expansion. Receiving this signal, the servo mechanism (35, 36, etc.) is actuated so that the internal pressure Pri of the cylinder chamber 32 becomes a pressure value (<Pr1) corresponding to the deviation signal S2. Therefore, it is possible to maintain the clearance between the upper die and the lower die at the bottom dead point, at a set value against such changes of the bottom dead point position. As described above, the present invention includes the hollow cylindrical member 20, the bolt member 21 which is an contraction force applying means, the cylinder unit 30, the hydraulic pressure supply means, the bottom dead point setting means 43, the bottom dead point position detecting means 45 and the correction control means 41, 42, and the changes of the bottom dead point are automatically corrected by adjusting the amount of contraction of the hollow cylindrical member 20. Thus, it is possible to automatically correct the changes of the bottom dead point position during the operation of the mechanical press quantitatively with high accuracy, thereby maintaining predetermined product accuracy stably at a constant value. The bottom dead point position detecting means 45 is constructed to detect the changes of the bottom dead point indirectly by detecting the clearance between the slide 4 and the bolster 5 according to the relation with the bottom dead point position setting means 43. Thus, it is possible to automatically correct the bottom dead point directly and it is also possible to correct the changes of the bottom dead point position due to the changeover or variation of the press speed as well as changes of the temperature. The hollow cylindrical member 20 is elastically expanded or contracted in the range of δr(= b - a) shown in Fig.4 in order to correct the slide bottom dead point position. Thus, the slide 4 is not lowered unlimitedly thereby enabling the correction of the bottom dead point position. If the hollow cylindrical member 20 is expanded or contracted, the female screw 20S of the hollow cylindrical member 20 and the male screw 16S of the adjusting screw shaft 16 apply pressure to each other along the axis thereof in order to fix the adjusting screw shaft 16. Thus, the bottom dead point position correcting apparatus is capable of acting as a fixing means for the adjusting screw shaft 16. The construction of the bottom dead point position detecting means 45 or the like is not restricted to the above mentioned example and can be selected arbitrarily. The construction of the mechanical press is not restricted either. (Second embodiment) Fig.5 shows the second embodiment of the present invention. In the bottom dead point position correcting apparatus according to the second embodiment, the shrink member 20 comprises a piezo actuator 30A which demonstrates piezo electric effect and the contraction force applying means comprises a high voltage power supply 46 which is a piezo driving means for forcibly expands or contracts a piezo actuator 30A by applying high voltage thereto, a charge input circuit 47 and a charge releasing circuit 48. The correction control means includes the signal comparison means 42A for comparing the set bottom dead point position signal Ps which is set on the bottom dead point position setting means 43 with the actual bottom dead point position signal Pi which is detected by the bottom dead point position detecting means 45 and for outputting the deviation signals S2, S1 to the charge input circuit 47 and the charge releasing circuit 48. The bottom dead point position correcting apparatus drives the piezo driving means 46, 47, 48 according to the deviation signals S1, S2 to automatically adjust the amount of contraction of the piezo actuator 30A, thereby correcting the changes of the bottom dead point. The other component of this apparatus, for example, the hollow cylindrical member 20, is fixed to the slide 4 by a bolt member having the same construction as the bolt member 21 and a piezo actuator 30A is provided between the slide 4 and the hollow cylindrical member 20, instead of the cylinder unit 30. According to the above-mentioned construction, the distance between the slide 4 and the die-height adjusting screw mechanism, the distance containing the piezo actuator 30A, is adjusted so as to eliminate the changes of the bottom dead point position. Thus, as in the first embodiment, the present embodiment makes it possible to automatically correct the slide bottom dead point position rapidly and accurately with the die-height adjusting screw mechanism being fixed, even during the operation of the mechanical press.

Claims: A mechanical press including an apparatus for correcting the bottom dead point position of the slide of said press wherein a die-height adjusting apparatus comprising a screw mechanism (16, 18, 19) is provided between the connecting rod (11) and the slide (4) of said press and is adapted to loosen a lock nut (22) for the adjustment of the die-height and to tighten said lock nut (22) when the adjustment thereof is completed to fix said screw mechanism (16, 18, 19), comprising a cylindrical shrink member (20) which is provided between said die-height adjusting apparatus and said slide (4) and which is adapted to be expanded or contracted along the direction in which the slide bottom dead point position is changeable, contraction force applying means (21, 30, 34, 36) for applying contraction force to said shrink member (20) which is provided between said die-height adjusting apparatus and said slide (4), a bottom dead point position detecting means (45) for detecting the bottom dead point position of said slide (4), a bottom dead point position setting means (43) for setting the bottom dead point position of said slide (4), and a control unit (41) for controlling the driving of said contraction force applying means (21, 30, 34, 36) in a manner to bring a set value of said setting means (43) into coincidence, with a detected value from said detecting means (45). The press according to claim 1 wherein said contraction force applying means (21, 30, 34, 36) comprises a cylinder unit (30) disposed between said shrink member (20) and said slide (4), a bolt member (21) extending through said shrink member (20) and in which the bottom end thereof is fixed to a piston (33) while the top end thereof is in contact with the top end of the lock nut (22) above said shrink member (20). The press according to claim 1 wherein said contraction force applying means (21, 30, 34, 36) comprises a piezo actuator (30 A) disposed between said shrink member (20) and said slide (4), a bolt member (21) extending through said shrink member (20) and in which the bottom end thereof is fixed to said piezo actuator (30 A) while the top end thereof is in contact with the top end of said lock nut (22) above said shrink member (20), and a piezo driving device (46) for expanding or contracting a piezo element by applying high voltages to said piezo actuator (30 A).

Inventors: SATO MITSUO, YAGI TAKASHI, SATO, MITSUO, YAGI, TAKASHI
Applicants: AIDA ENG LTD, AIDA ENGINEERING, LTD.
Application year: 1994
Main classification: B30B15
IPC codes: B30B15